In a wiring board to be used for semiconductor packages (hereinafter referred to as “interposer”), it is general to perform a large number of drilling processing for interlayer connection of wirings. In consequence, a laminate plate for interposers is required to have high drilling processability.
Now, for a laminate plate for semiconductor packages, there have hitherto been used a lot of curable resin compositions composed of a bismaleimide compound and a cyanate resin (for example, Patent Document 1). This is because in view of the fact that the subject resin compositions are excellent in heat resistance, the resin compositions were suitable as a resin composition for the laminate plate for semiconductor packages, which is frequently exposed to high temperatures in a reflow step or the like at the time of mounting.
However, in recent years, requirements for thinning and weight reduction of electronic appliances are increased, and associated with rapid progress of thinning and high density of semiconductor packages, laminate plates for semiconductor packages have also been required to have higher characteristics other than heat resistance over broad regions.
Above all, in order to suppress an increase of a warp at the time of mounting to be caused due to thinning of a semiconductor package, it is strongly required to make a coefficient of thermal expansion of a laminate plate for semiconductor packages close to that of a silicon chip, namely to realize low thermal expansion.
While there are considered a variety of techniques for realizing low thermal expansion of the laminate plate, it is effective to allow a resin per se for laminate plates to realize low thermal expansion, or to fill an inorganic filler in a high density in a resin composition. For that reason, a novolak type cyanate resin is used, or a content of the inorganic filler is increased (for example, Patent Document 2).
But, the use of a cyanate resin or the filling of an inorganic filler in a high density involved such a problem that cutting properties of the resin composition are lowered, thereby significantly impairing drilling processability of a laminate plate using such a resin composition.
Then, there was made an attempt to prevent a lowering of the drilling processability by adding a plate-shaped filler such as burnt talc, etc. as an inorganic filler or reducing a content the inorganic filler (for example, Patent Document 3). However, there were such inconveniences that the effect for preventing a lowering of the drilling processability is insufficient; the resin composition becomes low in elasticity, so that the effect for suppressing a warp of the semiconductor package is insufficient; and so on. Thus, satisfactory results have not been obtained yet.
In order to realize low thermal expansion of the laminate plate, it is effective to increase a content of a filler having a small coefficient of thermal expansion, such as silica, among inorganic fillers in the resin composition used in the laminate plate. But, if the content of a hard filler such as silica is increased, there was encountered such a problem that the drilling processability of the laminate plate is lowered.
Also, in order to enhance the drilling processability, there is made an attempt to add a metal dichalcogenide such as molybdenum disulfide as an inorganic solid lubricant particle (see, for example, Patent Document 4). But, if molybdenum disulfide is added, there is encountered such a problem that electrical insulating properties of the laminate plate are significantly lowered. Thus, satisfactory results have not been obtained yet.
Then, in order to solve this problem, the present inventors investigated additives which even when an inorganic filler is filled in high density, can inhibit the deterioration of the drilling processability and then found that a molybdenum compound has an excellent effect.
But, since the molybdenum compound has a large specific gravity, when added directly to a resin composition varnish to be used for the fabrication of a laminate plate, it easily precipitates to cause defective manufacture. For that reason, it is recommended to use a particle having a molybdenum compound supported on talc or the like (for example, KEMIGARD 911C, manufactured by Sherwin-Williams Company) (see, for example, Patent Document 5). However, there are such drawbacks that the resin composition varnish is thickened; aggregation of the molybdenum compound-supported particles with each other easily occurs; and so on. Thus, satisfactory results are not obtained.